The present invention relates to the field of drop deflection and has specific application to a recording or printing device in which one or more jets of ink are controlled to enable drops to be directed from each jet drop stream to a plurality of print positions on a moving print receiving medium. Further application may be made to drop dispensers or to particle separation.
A number of prior art jet printers have provided for servicing a plurality of print positions on a print receiving medium with each of a plurality of jets. Such printers have generally been relatively complicated in that a charge electrode assembly has been required for selective charging of drops in the jet drop streams, with the charge electrode assembly being separate from the deflection electrode assembly which provides a field to deflect charged drops in each jet drop stream. In one type of jet printer, shown in U.S. Pat. No. 3,739,395, issued June 12, 1973, to King, a plurality of jets, arranged in a row perpendicular to the direction of movement of the print receiving medium, are selectively charged on a binary basis. Two pairs of deflection electrodes, associated with each jet, generate orthogonal deflection fields through which the drops in each jet pass. The uncharged drops pass through the fields in a straight trajectory and a strike catcher extending beneath the row of jets. The first deflection electrode pair provides a static electrical field which deflects the charged jet drops in a direction substantially perpendicular to the row of jets such that they do not strike the catcher. Thereafter, the charged drops pass through a field provided by the second pair of electrodes and are laterally deflected in a direction parallel to the row of jets such that they strike the print receiving web at one of a plurality of print positions on the web. A cyclically varying potential is applied to the second pair of electrodes such that a cyclically varying electric field deflects charged drops to the print positions in a repeated sequence. Drops are in the cyclically varying deflection field for a substantial period of time, and some are exposed to the deflection field as it initially increases and then decreases. In some cases, the field may totally reverse during the time that a drop traverses the field. As a result, it may be difficult to produce deflection of the drops to preferred print positions.
In a different type of ink jet printer, such as shown in U.S. Pat. No. 4,307,407, issued Dec. 22, 1981, to Donahue et al, drops are subjected to a static deflection field to produce deflection to various print positions. The charge level carried by the drops is selected to produce deflection to the desired print positions or to a catcher structure. A charge electrode plate, separate from the balance of the printer structure, is required in the Donahue et al device to accomplish charging of the drops. In this device, as in most other prior art printers, drops are charged by applying an electric charge potential to a charge electrode positioned adjacent the fluid filament from which the drops are formed. The print head and the fluid filament are electrically grounded and, as a consequence, an electrical charge, proportional in amplitude to the electric charge potential on the charge electrode but opposite in polarity, is formed on the end of the fluid filament. This electric charge is carried away by a drop as the drop separates from the end of the fluid filament. An insulating space, downstream from the charge electrodes, must be provided to separate the fluid filaments from the deflection field or fields. This results in a fairly long drop path from the point of drop break off to the print receiving medium. This substantial distance can accentuate errors where the fluid filament is initially crooked due to imperfections in the print head.
Typical prior art in the areas of drop dispensing and particle separating is shown in Fulwyler U.S. Pat. No. 3,380,584 and in Robertson U.S. Pat. No. 3,647,138.